Copper in non-asbestos-based friction materials for brake pads provides many useful properties and performance characteristics including excellent reinforcing strength, increased friction coefficient at high temperatures and excellent heat transfer properties. In addition, copper provides many other qualities that increase the longevity of the friction material and the components the friction material engages, as well as reduces brake dust. However, copper is expensive and thus those of skill in the art look for more cost effective materials for use in brake pads.
Non-asbestos materials for brake pads also commonly include titanates, for example the friction materials of U.S. Pat. No. 6,656,240 to Chiba et al. Titanates can provide high temperature stability comparable to asbestos type materials. Titanate materials, such as hexatitanate and octatitanate, are useful since they coat the rotor surface with a uniform and consistent transfer layer. However, like copper, titanates are also expensive and thus those of skill in the art look for more cost effective materials for use in brake pads.
Steel fibers have been used in place of copper and titanates in non-asbestos friction materials for brake pads. U.S. Pat. No. 6,220,405 to Kesaven et al discloses examples of copper-free friction materials including steel fibers. However, steel fibers do not have many of the positive attributes of copper and are more frictionally aggressive, thereby increasing the amount of wear on the rotor against which the friction material engages. Steel fibers also generate dust that can quickly and permanently stain the surface finish of the rims of a vehicle.
Copper-free, non-asbestos brake pad materials including high amounts of dust have also been developed. U.S. Pat. No. 6,617,375 to Kobayashi et al discloses examples of copper-free, non-asbestos friction materials including high amounts of cashew dust. However, the processing of such materials provides high scrap rates and requires other costly process steps.